Kazuma Matoba heads the affluent Matoba Group and is the father of Shin and Rie Matoba. His family’s life was shadowed by tragedy when Grimms—entities tied to cursed weapons—attacked them, killing his wife and gravely injuring Shin and Rie. Though Shin eventually healed, Rie’s psychological scars confined her to long-term hospitalization. Following the assault, Shin inherited the Shiryu, a hereditary cursed weapon, and grew obsessively protective of Sayaka Ogata, his classmate and daughter of Amon Ogata. His jealousy spiraled into hostility toward Gai Ogata, whom he viewed as a romantic rival, triggering violent outbursts and a solitary crusade against Busoma-related threats.